Art Cashin: This is a big 'wild card' for global markets

They can't quite live up to what they were hoping to do, says Art Cashin of UBS, talking with CNBC's Mary Thompson about the ECB's policy announcement on Thursday. They may cut rates but they only have a few basis points to do that, says Cashin.

The bond market has already prepared for a negative market reaction to the European Central Bank's important policy meeting Thursday, veteran trader Art Cashin told CNBC on Wednesday.

"That is quite widely felt in bond circles," said Cashin, UBS' director of floor operations at the NYSE. "That they can't quite live up to what they were hoping to do. They can't do [quantitative easing]. Structurally, they're just not set up for it."

With the S&P 500 reaching another record high Wednesday morning, stocks could suffer an initial pullback on news from the ECB meeting Thursday unless there's a "major reaction" in the euro, Cashin said. That scenario remains a "wild card," he added.